#include <bits/stdc++.h>
using namespace std;
vector<double> f = {261.6, 294.3, 3270., 348.8, 392.4, 436.0, 490.5};
vector<string> r = {"C4", "D4", "E4", "F4", "G4", "A4", "B4"};
int main(){
  int N;
  cin >> N;
  vector<int> A(N);
  for (int i = 0; i < N; i++){
    cin >> A[i];
  }
  vector<long long> S(7, 0);
  for (int i = 0; i < N; i++){
    int c = N / f[i];
    for (int j = 0; j < N - c; j++){
      S[i] += abs(A[j] - A[j + c]);
    }
  }
  int p = 0;
  for (int i = 0; i < 7; i++){
    if (S[i] < S[p]){
      p = i;
    }
  }
  cout << r[p] << endl;
}